S.D.M. Jacques

Dynamic X‐Ray Diffraction Computed Tomography Reveals Real‐Time Insight into Catalyst Active Phase Evolution

Metals and metal oxides anchored to porous support materials are widely used as heterogeneous catalysts in a number of important industrial chemical processes. These catalysts owe their activity to the formation of unique metal/metal oxide support interactions, typically resulting in highly dispersed actives stabilized in a particular electronic or coordination state. They are employed in fixed-bed reactors as extruded or pelletized millimeter-sized “catalyst bodies” minimizing pressure drops along the length of the reactor. Since the efficiency of the whole catalytic system depends on the behavior and efficiency of the catalyst body per se, its design has very great importance. Crucial to this design is an understanding of the factors which influence the distribution and nature of the active phase during preparation. The type of desired distribution is very much dependant on catalytic process and required products; for example, an egg-shell distribution (as opposed to uniform, egg-white, or egg-yolk), where the active phase is located at the edges of the catalyst body, can be favored if the product forms readily.

Spatiotemporal multitechnique imaging of a catalytic solid in action: phase variation and volatilization during molybdenum oxide reduction

Caught in the act: A novel combined experimental setup is demonstrated, which uses very high energy/flux synchrotron X-rays and allows the measurement of spatiotemporal data on larger reactors and the use of techniques such as fluorescence spectroscopy and Compton scattering. Wide-angle X-ray and Compton scattering reveal information on the causes of molybdenum volatilization in partial oxidation catalysts.

A new approach to synchrotron energy-dispersive X-ray diffraction computed tomography

A new data collection strategy for performing synchrotron energy-dispersive X-ray diffraction computed tomography has been devised. This method is analogous to angle-dispersive X-ray diffraction whose diffraction signal originates from a line formed by intersection of the incident X-ray beam and the sample. Energy resolution is preserved by using a collimator which defines a small sampling voxel. This voxel is translated in a series of parallel straight lines covering the whole sample and the operation is repeated at different rotation angles, thus generating one diffraction pattern per translation and rotation step. The method has been tested by imaging a specially designed phantom object, devised to be a demanding validator for X-ray diffraction imaging. The relative strengths and weaknesses of the method have been analysed with respect to the classic angle-dispersive technique. The reconstruction accuracy of the method is good, although an absorption correction is required for lower energy diffraction because of the large path lengths involved. The spatial resolution is only limited to the width of the scanning beam owing to the novel collection strategy. The current temporal resolution is poor, with a scan taking several hours. The method is best suited to studying large objects (e.g. for engineering and materials science applications) because it does not suffer from diffraction peak broadening effects irrespective of the sample size, in contrast to the angle-dispersive case.

Interlaced X-ray diffraction computed tomography

A new data-collection strategy for Xray diffraction computed tomography experiments is presented that allows, post experiment, a choice between temporal and spatial resolution.

An eye on the inside: imaging of catalytic particles under reaction conditions

electrode materials. Guy Ouvrard, Miloud Zerrouki, Christian Masquelier,, Mathieu Morcrette, Stéphane Hamelet, and Stéphanie Belin, c a Institut des Matériaux Jean Rouxel,Université de Nantes -CNRS, Nantes, France, b Laboratoire de Réactivité et de Chimie des Solides, CNRS Université de Picardie Jules Verne, Amiens, France, c Synchrotron SOLEIL, Gif s/ Yvette, France E-mail: guy.ouvrard@cnrs-imn.fr